1. Field of the Invention
The present invention relates to a secondary air supply device, incorporated into an intake air cleaner of a vehicle's engine, for supplying secondary air into an exhaust system of the engine.
2. Background Art
Japanese Utility Model Laid-open No. Hei 5-6148 discloses a secondary air supply device disposed inside of a main air cleaner's case, hereinafter referred to as a main case. The main air cleaner is divided into a dirty side and a clean side by an air cleaner element, hereinafter referred to as a main element. The secondary air supply device is formed as a small region, or part, of the main element located on the clean side.
Japanese Utility Model Laid-open No. Sho. 61-80310 discloses a secondary air supply device in which an inlet of a sub-air cleaner is provided inside the clean side of the main air cleaner. The sub-air cleaner uses the main case and the main element.
In the structure disclosed in Japanese Utility laid-open No. Sho. 61-80310, since both the main air cleaner and the sub-air cleaner use the clean side, the sub-air cleaner must be kept away from the influence of negative pressure caused by air intake of a carburetor of the engine. Therefore, the sub-air cleaner must be positioned away from the intake inlet of the carburetor on the clean side. This results in the clean side being required to have a large capacity, which reduces design freedom.
In the structure disclosed in Japanese Utility Laid-open No. Hei 5-6148, the negative pressure influence due to the carburetor's intake is avoided. However, the shape of the main element must be adapted to accommodate the secondary air supply device. Therefore, the possible structural configurations of the main element are limited, and it is difficult to use a generally cylinder type of main element.